Computers, televisions, communication devices, consumer electronics and the vast majority of electronic equipment rely upon the printed circuit board (PCB) to interconnect and interface internal electrical components. For example, the PCB known as a computer motherboard provides interconnection and interface between memory stores, processors, switches and a host of other components that collectively operate as a desktop or laptop computer. In other words, a PCB is the platform to which other electronic devices are commonly attached so as to interact as a greater system or device.
Early PCB's were relatively simple as the number of components was low and the size and complexity of the attached components were also relatively simple. As electronic components and apparatuses, such as cell phones and personal data assistants, became smaller, thinner and more advanced in performance ability, PCB's for such devices have become more complex and higher density.
With advancements in nano-scale fabrication of semiconductor devices, more and more components may be desired upon a PCB. Contemporary PCB boards often require high resolution manufacturing techniques and precision. In addition, whereas once the interconnection circuits on a PCB were commonly on only one surface, modern system often require at least two layers. In some instances this may be achieved by providing a PCB with a circuit trace on both the top and bottom surfaces, generally requiring either two substrates to be joined as a single PCB, or careful fabrication processes so as to not foul one side while rendering the other, and/or multi-level fabrication.
The fabrication process for a conventional PCB is typically quite involved. An insulating substrate is provided with a thin copper (or other conductive metal) layer deposited across the top surface. To function as a PCB, the circuit or trace lines need to be defined. One typical method used to establish the trace lines from the metal layer is the well known process of photolithography.
Generally speaking, a photo-resist layer, also commonly known simply as a photoresist, or even resist, is deposited upon the metal layer, typically by a spin coating machine. A mask is then placed over the photo resist and light, typically ultra-violet (UV) light is applied. During the process of exposure, the photoresist undergoes a chemical reaction. Generally the photoresist will react in one of two ways.
With a positive photoresist, UV light changes the chemical structure of the photoresist so that it is soluble in a developer. What “shows” therefore goes, and the mask provides an exact copy of the patterns which are to remain—such as, for example the trace lines of a circuit.
A negative photoresist behaves in the opposite manner—the UV exposure causes it to polymerize and not dissolve in the presence of a developer. As such the mask is a photographic negative of the pattern to be left. Following the developing with either a negative or positive photoresist, blocks of photoresist remain. These blocks may be used to protect portions of the original metal layer, serve as isolators or other components.
In typical PCB fabrication, the photoresist blocks protect portions of the metal layer as an etching process is performed. It is generally understood that an etching process such as ion etching, is accomplished by either of two traditional processes, a physical process or an assisted physical process. In a physical etching environment no chemical agent is provided. Rather, the removal of material is entirely dependent upon the physical impact of ions knocking atoms off the material surface by physical force alone. Physical ion etching is commonly referred to as ion milling or ion beam etching.
In an assisted physical process, such as a reactive ion etching process (or RIE), removal of material comes as a combined result of chemical reactions and physical impact. Generally the ions are accelerated by a voltage applied in a vacuum. The effect of their impact is aided by the introduction of a chemical that reacts with the surface being etched. The reaction makes the surface softer and as such, increases both the relative control of the etching as well as the etching rate.
Once the etching process is complete, the remaining photoresist blocks are removed, normally by dissolving them with a chemical agent. If a trace is intended to cross another trace, a dielectric layer may be applied, followed by another application of photoresist to be masked, exposed and etched so as to insulate portions of some traces while providing contact spots for other traces. Typically a multi layer PCB board is achieved by laminating multiple thin layers together, each layer having previously lithographically established traces.
Although the photolithographic process has been described in general terms, it is still apparently obvious that it is a complex and involved process. As it is a process involving the removal of material (the metal being etched as well as the photoresist) it is also a somewhat wasteful process. Recapture of materials for re-use may or may not be economically feasible. In addition, many of the materials and chemicals used may be harmful to the general environment.
Further still, the multiple steps are time consuming. It is also not uncommon to experience some percentage of failure due to defects in the masking and etching process which may or may not be detected prior to the final PCB being provided for testing and or component assembly.
Although current PCB architecture is largely aided with computer drafting, it is not uncommon for prototype systems to require several versions and revisions to a PCB. Indeed, with a new system, or simply to test new semiconductor structures such as memory devise and processors, it is not uncommon to utilize repeated copies of the same PCB architecture and or to rapidly evolve the PCB architecture as refinements are made with the attaching components. As such the time, cost, materials and other factors of the photolithographic processes traditionally used in PCB fabrication may be aggregated and aggravated.
Hence, there is a need for a system and method of rendering PCB's that overcomes one or more of the drawbacks identified above.